Method of making cast ceramic flatware



J. A. BQWER METHOD OF MAKING CAST CERAMIC FLATWARE l Feb. 17, 1942.

Filed Feb. 27. 1939 2 Sheets-Shee. 2

'INVENTOR /zwn/ /WM/V Patented Feb. 17, 1942 UNITED STATES PATENToFFicE;

METHOD F` MKING CAST CERAMIC FLATWABE James A. Bower, Chester, W. Va.,assignor'to The Taylor, Smith- & Taylor Company, a corporation of WestVirginia Application February 27, 1939, Serial No. 258,746

' 9 Claims.

and unlugged cups, bowls, napples, platters -and pressed ware.

It specically excludes those itemsof hollow ware from which a corecannot be removed; e. g., sugar bowls, cream pitchers, teapots,l saltsand peppers and some casseroles, 'gravy boats, etc.

The hollow ware articles are usually produced by the conventional.one-sided casting process which is incapable of producing articles ofnonuniform thickness. Most of the articles included by the term ilatwareasabove dened are produced by jiggering; in some cases pressing isresorted to. Lugs or handles are produced separately and then attachedprior to tiring. As jiggering is less expensive than casting thepractice has beento produce by jiggering all articles capable of beingso made.

- Jiggering and casting procedures as practiced in the ceramic industryare both well known and are bothwidely utilized. In the jiggeringprocedure. a suitable clay is mixed with water toa ilowable consistency,and after thorough agitation is passed through a illterpress. Thisproduces lter'cakcs which are of greatly4 reduced water content and ofthe general consistency of modelling clay; i.' e., are plastic.These-lter cakes are stacked and allowed to age, the aging processresulting in a deilnite improvement in the quality and Vnature of theclay for som'e rea- .son which is not well understood but which probablyis related to air content or possibly bacterial action; y

Subsequent to the aging procedure, the clay is put through a pug millwhich extrudes it in the form of a continuous bar or column which is cutoil' at intervals by .a wire or the like to produce a so-called pug.These pugs are then conveyed to the jiggering departmentwhere portionsof the pugs .are deposited one at. atimelby hand upon-a mold andiiattened 'into -a pancake-like form b`y a suitable tool,- called abatt, wielded by an operator. Then a forming 1500i (ligger) is lowtom oroutside of the plate, dish, or the like; Then the crude article and themold, which latter is so contoured as to produce the desired design,pattern, etc.v on the top or inside of the plate or dish, are removedland placed in a drying zone fora period of time and at a suilcienttemperature to cause the jiggered clay article to acquire a leather-likehardness, after .which it is iired in a kiln and subsequently glazed,decorated, or the like-and'again red to produce the finished article.

The productionof certain'ceramic articles by' pressing involvesindividual` manual operations for each article or piece of ware. In handpressing procedures `the article or piece of ware cannot be providedwith a foot nor can it have portions of .different thickness than otherportions.

y'Ifhese limitations on hand Ipressing operations greatly restrict thevalue and use of vsuch procedure.

` Such articles of ceramic ware which can not be made either bythe'jiggering or 'by the presslng procedure are made bycasting. Incasting ceramic articles as now practiced, a' mold is prepared ofplaster of `Paris or other suitable absorbent material which isdehumidlfed and .which has an inner surface complementary to the outersurface to be formed on the cast article. Then liquid slip of thecorrect specific gravity approximately 1.74 being preferred) andviscosity is poured into the mold sufllcient to fill the same.'

This liquid slip may be made up by blunging the filter cakes abovedescribed with water to reduce the consistency of such to that of lapaint. The liquid slip is allowed to remain in vthemold for a deiiniteperiod of time dictated by judgment and experience and during thisinterval the mold absorbs moisture from that.` part of the liquid slipin contact with the mold wall to form a more viscous, heavy layer orlcasting which adheres to the mold wall. After' the allotted time theexcess or still liquid slip is poured out or removed, and thisleaveswithin the mold a rather soft casting adhering to the mold wall. l

This mold and casting are then yplaced in a drying zone for such timeand at such temper-' ature as to cause the casting to acquire a"leathmom surfaces, .at which time 'the casting is capaered into contactwith the clay on the mold and. A

the mold rapidly rotatedgthus forming the boter-hard condition and toshrink away from the ing its true procedural nature.

The possibility of this xiiiv in ine mold cavityby pumping the samethrough pipe lines, thus also eliminating the usual handling and truck--ing of the pug'ged clay to the various plant locations where it is tobe used.

While the invention is capable of being carried out in an automatic orsemi-automatic manner, for the purposes of brevity and convenience Iwill describe the invention in the form in which it can be carried outbyhand, thus demonstrat- I assemble one or more sets of dehumidiiiedmolds, one set of which has been illustrated inFig. l. In this gure theset of molds consists of an upper mold part 'I0 and a lower mold partII. These two mold parts are so configured as to produce be,- tween thema mold cavity I2 which is of slightly greater. sizethan and thesameshape as the ceramic article to be produced to allow for shrinkage infiring. 'I'his mold Vcavity I2 occupies the central innermost .portionsof the mold parts IIi and II, and, as will be understood, the innerperipheral portions of the molds abut and seal off the mold cavity asindicated by the parting lines I3. Suitable means may be provided forensuring accurate registration of the molds.

Each mold part I and II is composedof a plaster of Paris or othersuitable composition which, prior to use, has been manitained under suchconditions of temperature and humidity as to produce a high degree ofmoisture attraction in the composition. It is not usually necessary tomaintain the mold parts in a bone-dry condition causing interferencewith the pouring' operation beca"se the molds are equally effectiveinabsorbing moisture when their moisture content is low,

so long as the percentage of moisture is materially less than that ofthe slip. As will be appreciated from Fig. l, the mold cavity includes acentral portion I4 which is, in the particular instance shown,disk-shaped and gradually de.

creasing in thiclmess toward the center. Circumferentially bounding theupper (in Fig. l) surface of cavity portion I 4 is an inverted U- shapedmold cavity portion I5 which is adapted to form the foot of the ceramicarticle. Beyond portion I5 the mold cavity has an arcuate radiallytapering portion I6 Aof annularnature which is adapted to form the bowlof the ceramic article. Beyond portion I6 themold cavity again curvesand tapers until it terminates in the reduced portion I'I which isadapted to form the rim of the ceramic article and the portion adjacentVthe rim.

It is to be understood that the mold cavity described as well as thearticle hereinafter specifically referred to is merely one example of aceramic article which can be produced in accordancev with the presentinvention and is therefore to be considered purely as exemplary and notin any sense as restrictive or limitative.

'Referring again to the set of molds of Fig. l,

it will be clear that a pouring hole I8 is provided in the upper moldpart III. This opening prefer ably tapers forthe accommodation of afunnel I9, this funnel closely fitting the hole Il so that there is noair space between and no possibility of causing or permitting slip to-get out -of the mold cavity. I n addition, the funnel is prefermay beminimized or eliminated by carrying out the entire pouring operation ina vacuum, and it is to be understood that this forms a definite butanoptional part of the present invention because at least under someconditions it is not l essential to pour the slip under a reducedatmospheric pressure. In pouring liquid slip under ordinary atmosphericpressure conditions I have found that the air in the mold cavity isdisplaced rapidly and effectively by the incoming liquid slip and thatthere is substantially no pick-up of air by the slip,l the air in themold cavity passing into the molds themselves due tothe comparativeporosity of these molds As hereinafter explained pouring may takeplacein a closed system and/or under increased pressure. As will be drawingsthat the pouring point isv at or near the portion of the cavity whichproduces the thickest portion of the ceramic article and iiow of slipproceeds in a 'thick-thin, direction, therefore,

relative to mold cavity dimensions. This I have Afound to be ofimportance. Pouring liquid slip in such manner prevents any interferencewith the vcomplete iilling of the cavity, thus eliminating thepossibility of a portion of the slip in a nar'- rower part of the cavitysolidifying andobstructing the path of the incoming slip. For example,experiments which I have carried out wherein vliquid slip has beenpoured at the center of the mold cavity have demonstrated thatinvariably liquid slip will harden atvone or more spots within the moldcavity portion Il, and this absolutely prevents the production of asatisfactory article.

The point of pouring can be either adjacentA the portion I5 ofthe moldcavity or may be at portion l I5' as indicated in Fig. 4 wherein funnelI9' discharges slip directly to mold cavity portion I5. I prefer,however, to pour at approximately fthe point indicated in Fig. las Ihave found that under average conditions this produces the bestcastingwith substantially no imperfect articles. The pouring hole shouldbesmall and thus I can produce a casting with only a very small pour spot20 to be later removed and finished.

The pouring operatlonjis continued until the mold cavity is filled anduntil sumcient excess accumulates-in the funnel to produce vonly a smallpour spot when the excess is utilized due to elimination of water fromthe slip during the casting period. For example, I have-determined thatthere is a weight shrinkage of about 48% involved and that this weightshrinkage is ac'- companied by a volume shrinkage of) about 31%.

. These figures depend uponthe speciiic gravity ofV the slip andthenature of the materials. I then transfer the slip-filled set of moldsinto a drying zone and the liquid slip is allowed to remain in the moldslfor alpredetermincd length of time which is determined by experienceand Judgment depending upon the size of thel mold, the size oi' themolil cavity, the percentage of moisture in the molds' and slipand otherfactors such as will be appreciated by those versed in this field. 'I'heaction which takes place when the slip is poured into the mold cavity iswellknown and needs no detailed description here. Briefly, the moldsattract moisture from the slip and this moisture is later removed fromthe molds when the molds are reconditioned. Usually a mold must be driedbefore each use thereof. It will also be understood that the molds areof sumcient volumetric capacity, insofar as their moisture absorbingcharacteristics are concerned, to hold the moisture extracted from acharge of slip and that these molds are subsequently dehumidifled beforethey are used again. The pouring or filling op-v eration usuallyrequires about -20 seconds and casting is complete in about 20 minutes.

Under some special circumstances I have found that the action can beimproved or controlled by making one mold part of a different density orof different moisture content than the other. The advantages which thesevariations of my procedure will produce will be understood but such isparticularly useful in connection with ceramic articles of odd orpeculiarv shapes or wherein certain portions of the articles are of'much greater thickness than other portions, and

thus it is not necessary to prolong the drying' operation for suchexcess time as would normally be necessary to produce the requiredamount of moisture removal from the thickest portion of the casting.Hence, uniform drying and residual moisture content can be produced inarticles of difcult or unusual shape, size, etc.

VIn connection with filling the molds with liquid slip, I also wish topoint out that in prior commercial casting procedures excess slipisalways poured greatly in excess of actual requirements.

4This not only represents an uneconomic utilization of material and isundesirable as a result but also means that subsequent manual trimming,smoothing, etc. operations are lexcessive. In connection with my newcasting procedure, I complete the pouring operation `under closeobservation and control, and where an appreciable excess is noted thisis immediately removed by suction as by dipping the end of a suctionhose or nozzle into the slip until the level is lowered to minimize thesize of the pouring spot. Preferably, I pour only a slight excess ofslip, as will be understood from what has preceded. After the dryingoperation above referred to, the top mold part l0 is removed andthecasting has shrunk away slightly therefrom sothat the mold part maybe removed without damaging the surface of the casting. At such time Ialso prefer to flush out the funnel I9 so that it will be clean andready for a subsequent use.

The matter of mold release also forms an irnportant part of my inventionas care should be taken in removing the top mold lest the casting stickthereto and be ruined. I have discovered that by dusting the moldsbefore theyare lled with slip a positive mold release is secured andthat by suitably proportioning the amount of dusting of the moldsurfaces I can control the mold release so as to enable either 'moldpart to be removed first as desired. As dusting material I may employtalc, int, pyrophyllite or plaster of Paris in finely divided condition.Mold oil may also be used and is intended to be within the scope of theterm dustingl I make a suspension of any of the above or other suitabledusting materials usually in water -absorptive properties appreciablybut is enough to prevent sticking of slip or casting thereto. Byspraying somewhat more material on the upper mold an upper mold releaseand control are produced and this I have found preferable although it iswithin the scope hereof to spray more material on the lower mold where alower mold release is required as in connection with a'modification ofthe present invention which is set forth hereinafter.

The casting in its condition at this time is comparatively soft and cannot be successfully handled without deformation; therefore; I allow thecasting to remain on the bottom mold part I I for an additional periodof time and until the casting assumes a condition which is termedleather-hard, this term being one commonly used in this art to designatesuch a casting condition in connection with the casting of hollow wareasabove described. When the casting acquires the leather-hard condition itis then removed from the bottom mold and can be suce cessfully handledto a moderate extent without suffering damage or deformation. Thepouring spot which is indicated by the numeral 20 in Fig. 2 has beenremoved while the casting is still on the bottom mold and while this isa hand operation the same may be accomplished automatically orsemi-automatically as will be pointed out hereinafter. 'I'here isunavoidably lefta slight telltale mark or disguration on the articlewhich is distinctive but unobiectionable. denotes a cast article.

Preferably, the pouring spot 20 of the cast flatware article. 2| ,isremoved before the casting is removed from the bottom mold as juststated since this reduces the possibility of injury to the casting, butunder other conditions these steps may be reversed without disadvantage.It will likewise be appreciated from Figs. 2 and 3 that the plate 2l hasa foot 22, ball 23, and a rim 24, and that the various parts havedifferent thicknesses.

Having removed the casting from the mold, the molds are subjected to thenecessary dehumidicaton and/or cleaning and vare then ready to beutilized for-another casting in another cycle of operations. The castingmay now be finished in any suitable manner, depending upon its specificnature or the requirements of any given order. In producingsemi-vitreous ware, ordinarily the casting is fired in a kiln under theusual conditions to produce a hard but' dull and comparatively porous orabsorbent article which is then provided with a suitable liquid glaze bydipping or spraying operations and then v re-iired to produce the'finished article. These and spray the same on the inner mold surfaceswhich define the mold cavity prior to filling such cavity with slip. Theamount of dusting ma- Y terial used is not sumcient to clog the pores ofthe moldsurfaces or to reduce or slow down their steps result in theproduction of an article which is undecorated, so to speak, it beingunderstood that where a pattern is to be produced on the article, thismay be done in either of the conventional manners now employed; viz., bytransfer-,-

'to ware having a vitriiied body.

Referring to Fig. 5 of thev drawings, the'numeral 25 indicates apartible mold made of plas It invariably ter of Paris or the like landmaintained in a dehumidied condition, as already described in connectionwith mold parts Ill and ll. There are two mold parts identical withtheone shown at 26 in Fig. 5, and between then they form a mold cavity 21of the appropriate size and con-` figuration to form the cup indicatedat 28 in this figure. The mold arrangement 1n Fig. 5 differs, however,from-that of Figs. 1 and 4 heretofore described mainly in that there isa top mold part 29 of the same material which has an extension orcore 30between whichand the mold parts 26, already mentioned, the mold cavityis defined.

.For the purpose of assuring accurate registration between the side moldparts 26 and the top mold part 29, the same are. provided at theircontacting surfaces with the cooperating projectlng portions 3l andrecesses 32. Likewise, to

insure accurate registration at all times between the two side moldparts themselves interfltting Vlugs 33 are provided which line up thesemold parts perfectly, the lugs being preferably hemispherical in shape."It will, of course be understood that one side mold part is providedwith lugs 33 land that the other side mold part is provided withcomplementarily shaped recesses.

It will be observed further from Fig. that the top mold part 29isprovided with aconical opening 34 therethrough and that a copper orother non-porous funnel 35 is provided by means of which liquid slip,indicated at 36, is filled into the mold cavity and part way upthefunnel', as previously set forth, after the three molds areassembled.' The cup or casting indicated at 28 K increases somewhat inthickness from the top or rim 31 -thereof toward the base or bottom 38and the `cup is provided with an annular and somewhat iiaring foot 39.'The cup or casting 28 is also shown as having a. 'lug or handle l0,"

.the ceramic body there is a relatively large Vand ance with existingpractices.`

strong casting formed and thus the area where strongest part'of theceramic article instea of the weakest as in lugged ware madein Incarrying out4 the procedure of my present invention on luggedv orhandledware,v liquid slip ofsuitable compositionyviscosity and specificgravity, as explained above in connection with the casting of. lates,l`s poured into the funnel 35 and imme ately the `mold cavity rbecomessealed oi from the atmosphere due to the presence of the slip in thefunnel, as WHLbe-appreciated from Fig. 5.v The air in the mold cavitythe lug br handle joins the body is now. the Y acc rdmade by the usualprocedure which involves making atfleast twoparts anduniting them. Imay, if I so desire, carry out the pouring operation under reducedpressure of the order of about 27 5 inches of mercury, and I have foundin connection with the use of reduced pressure the vacuum should not beso nearly perfect as to cause boiling of the slip, which would be thecaseI if theV degree of vacuum approaches 29 inches (more or less) ofmercury.`

Both in connection with theuprodu'ction of 4lugged and unlugged ceramicware, plates, etc.. I mayand in some cases I prefer to-carry out thepouring operation in a closed system or under increased pre'ssure Thiscan be very readily accomplished-by providing funnel i9, -I or 35 with acover through which a tube or discharge pipe passes by means of whichthe liquid slip can be fed tothe lowerportion of the funnel. The use of'a closed system prevents entrainment of air by the moving liquid slip.The use of increased pressurey has the additional advantage that it vforcesthe slip into the mold cavityat an increased rate and thusshortens the time for the filling operation. I have found thatthere islittle or no danger that the slip will pick .up air L under theseconditions because of its highly viscous nature. Otherwise', theprocedure for making the-article( 'of Fig. 5 is the saine as already '30described with the exception that itis specifically pointed out thatpouring .takes place through the handle, although this 'may besomewhatvaried so long as pouring occurs at or L adjacent the thick or thethickest part of the casting ultimately produced.

In connection with the present/procedure l which, for the first time,'makes it possible to cast ceramic atware successfully and eiiiciently,I wish to point out that in contrastto prior art 40 methods lI canproduce a pattern or designeither out` the appropriate portions of thesurfaces of the mold parts which constitute. the mold cavity definingwalls. Where yan embossed design or pattern isto be made, this can bereadily-done by cutting out the appropriate portions of the moldsurfaces so that these cut out portions becomeiilled with slip andthusserve vto define raised portions of the casting. Where recessed or'intaglio designs or patterns are desired- 'in either faces .withadditional material of which the molds are composed, or when the moldcavities are initially cut or fiormedfrom themold composition'l` thiscan be taken into account at such a time.

duce Whatiain'effect, a new ceramic flatware artlcle.

is driven ,immediately into the mold parts and of non-uniformV thicknessor which vanes' in therefore no interference with-the pouringoperthickness at different. points or from point to 'ation occurs andthere is no entrapment of air point regularly or irregularlyfY This is anew and in thev slip with the consequent disadvantages unexpected resultyof my procedure andis a, result thereof, as also pointed opt elsewherein this which'can'notbaccomplished by any previously specification. Thetime during which the slip isA -knownor practlcedcasting procedure;Pouring becoming converted into a casting can be readily determinedorcalculated, and I have discovered' .in this connection that I canproduce a superior,

lugged or handled artic e of ceramic ware in a v much shorter time thanthe same ware can* be? 5 and of somewhat increased density due to the orboth surfaces of the 4ware, this can be accom- @55 plished by building pthe appropriate mold sur- Thus I have made it possible for the art topro.

elimination -of entrapped air, and also for such reasons the ware hereinproduced is characterized bygreater strength and better resistance tochip'- ping, cracking, and breaking. Articles which are unusual can beproduced due to the fact that embossed or intaglio patterns, designs,trade-marks, etc. may appear at any desired locations on any or allsurfaces and due to the nature of my prescnt invention I can alsoproduce thinner and ksomewhat lighter ware without sacrificing strength,appearance, or serviceability.

Ware produced in accordance with my present invention is very muchreduced in cost, is free from stress, warpage and distortion, lacks theusual pinholes, cracks, crevices. etc., and I have' found that ware castin accordance with this invention is not only much less expensive thanware cast in accordance with` prior procedures, but insome cases is madeas inexpensively or even somewhat more inexpensively than ordinaryjiggered ware of the same size and weight.

` I have mentioned above that my procedure may be carried out eithermanually or in an automatic or semi-automatic manner. In either of thelatter cases Iprovide a conveyorsuch as a series of movable trays andtravelling at an appropriate rate of speed. At the receiving end of thisconveyor sets of molds are spaced thereon such as those illustrated inFig. 1, and as these sets of molds are carriedvalong by the conveyor,

sure` is relieved after filling is completeso as to a pouring hose ornozzle,`which is provided for each set or row of molds, is lowered intosuch position that the same register with and project into the funnels,and for a short distance thereafter these nozzles move along with themolds and discharge the required amount of liquid slip during suchmovement, at the completion of which the nozzles are raised andretracted, ready to fill another row of molds and so on, or a row ofmoldsleach on atrayis stopped, lled, and started, thus resulting inintermittent mold movement. Also, such liquid` slip may be fed to thedischarge or feed nozzles or hose by a camactuated displacement pump ofsuch character as to be initially relatively slow and then relativelyfast to meet the requirements of the slowfast fill elsewhere described.In practicing the procedure in the automatic or semi-automatic mannerreferred to, at the time when the upper mold part is removed, this ispreferably placed on the conveyor alongside the 'other mold parts. Asthe conveyor travels it may pass through the necessary orrequisitedrying zone above referred to, and also as set forth above, the conveyormay pass through a vacuum chamber at the time when the pouring operationoccursso as to make sure that air is eliminated as far as possible. Itwill be understood from the brief examples set forth that all theoperations may be carried out upon a long conveyor and that suitablemechanical equipment and apparatus may be utilized to aid in effectivelycarrying out the process.

The slow-fast fill previously referred to in connection with pouringslip into -the mold cavity may be carried out either manually orautomatically. In the manual procedure pouringslip from a suitablecontainer is so effected as first to seal oif the mold cavity from theatmosphere with A liquid slip and for ordinary size plates'or flatwarethis occurs at the first drop or in a very fewA drops which, deliveredadjacentl the bottom of the funnel as they are, immediately ll themoldcavity below the fu'nnelbottom and rise up slightly in the funnel;then, the fill is completed speedily until the entire Y.mold cavity is full and fill the mold cavity under pressure and effect casting at normalatmospheric pressure, thus further differentiating from knowncastingprocedure in which the duration of the castirm step isaccompanied by they application of superatmospheric pressure.

The slow-fast `flll and the pressure changes described can also beeiected automatically (or semi-automatically) through a closure providedfor the funnel either by gravity or by a cam actuated piston type pump.In each case slip is fed under pressure to a tube extending to thebottom of the funnel firstrelatively slowly and then relatively rapidly,as already explained. The details of apparatus or its operation requiredfor such are not specifically described and claimed herein as the samevforms the basis of my copending application Serial No. 265,461, ledAprilv In carrying out corroborative tests and experiments I alsoproduces a line in the ware which is objectionable. This line is araised ridge or bead in the ware extending in a generally radialdirection. It seams to resultfrom an unduly long travel of slip aroundthe mold cavity in a generally circular direction from the point ofpouring and forms where the oppositely traveling streams of such slipmeet each other within the departed from slow-fast fill, the lling underof this spot is obscure the slow-fast fill overcomes it. I

In some cases also I lhave found it to be desirable to cast particulararticles upside-down. In carrying out this modification of the inventionthe molds of Figs. 1 and 4, for example, are invertedand a hole providedextending up through the lower mold into which the end of a hole, nozzleor the like is inserted so that filling takes place from below underpressure but also in the thick-thin direction as above explained. Insuch case I omit the funnel and all its accoutrements and, of course,Ithe pressure is continued or other suitable means provided forpreventing the slip \from running out until the casting has beenformed.- This procedure would preferably be carried out on a bench andis semi-automatic in its nature.

Within the terms of the appended claims, other additions, omissions,"lsubstitutions, and altera? tions may be-made without departing from theprinciples or. scope of the present invention. In connection with somearticles pouring may occur at two points and while this produces twopour spots the filling operation is speeded up and perfect fillingalways results regardless of size,

discovered that improper filling i the use of two diametrically oppo.

shape, contour, etc. of the article.k It is also within the scope of theinvention to pour at or adjacent the thickest and thinnest portions ofthe mold cavity. Rather the invention is to be defined by the appendedclaims. I

Having thus described. my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A method of casting ceramic ilatware which comprises introducing acharge of liquid slip of suitable composition, specific gravity andviscosity into a closed mold cavity of non-uniform thickness adjacentthe thickest portion thereof to fill the mold, causing such charge ofslipto iiow in a thick-thin direction and to take the form of a ceramicflatware article, withdrawing moisture from the charge of slip whilemaintaining its form to produce a well-denned casting, converting thecasting to a condition of leather-like hardness and then suitablynishing the casting as required, said charge introduction beinginitiated at a relatively slow rate and completed at a relatively fasterrate.

2. A method of casting relatively thin ceramic iiatware of non-uniformthickness which comprises the steps of introducing liquid slip ofsuitable composition into a closed mold cavity having the same shape asthe atware to be produced and at the thickest portion of such cavity,extracting moisture from such liquid slip to produce a casting ofincreased density as compared with the liquid slip, imparting to thiscasting sufficient strength to enable it to be poured through anon-porous funnel and the amountl of liquid slip introduced being s0cOntrolled as to constitute a volume sufficiently in excess of thevolume of the mold cavity to allow for shrinkage occurring during theformation of the casting while moisture extraction is proceeding, saidslip introduction being initiated at a relatively slow rate andcompleted at a relatively faster rate. i

3. In a method of producing thin ceramic flatware'by slip-casting thesame in a closed mold cavity` of non-uniform thickness characteristics,

the steps which comprise introducing liquid slip into such mold ,cavity4adjacent the thickest portion thereof in such manner that the initialportion of such slip Ais introduced relatively slowly and the moldcavityis thereafter filled at a rate faster than the rate at which suchinitial slip portion is supplied.

4. In a method of producing a thin ceramic flatware article byslip-casting the same in a tively slow rate as to the initial portionthereof,-

at a faster rate thereafter until the mold cavity is completely filledand finally supplying additional slip to said cavity to compensate vforthe absorption of water by said porous mold at the rate at which saidporous mold absorbs the water from said slip to complete the article.

5. `In a method of producing' a thin ceramicV ntware article byslip-casting the same in aporous mold provided with a closed mold cavityof non-uniform thickness in which the thickest portions communicate withthe thinner portions by portions of equal or diminishing thickness, thesteps which compirse introducing liquid slip into such mold cavityadjacent the thickest portion thereof in such manner as to effectfilling and casting in a thick-thin direction, the slip being'introduced into the mold Vcavity at a relatively slow rate as to theinitial portion thereof, at a faster rate thereafter untill the moldcavity is completely lled and iinally s upplying additional slip to saidcavity to compensate for the absorption of water by said porous mold atthe rate at which said porous mold absorbs the water from said slip tocomplete the article, that part of the iilling of the mold cavity whichis carried out at the faster rate being eifected atsuper-atmospheric.pressure which is subsequently relieved so that thesupply of additional slip occurs at substantially normal atmosphericpressure. l i

6. A method of slip-casting an article of ceramic iiatware, in which`liquid slip is fed to a closed mold cavity formed in a porous mold,which comprises initially delivering liquid slip into such mold cavityat a relatively slow rate, thereafter lling the mold cavity at a fasterrate and preventing the entrapment of air in the slip which is beingdelivered at such faster rate.

7. A method of slip-casting an article of ceramic iiatware, in whichliquid slip is introduced into a closed mold cavity formed in a porousmold, which comprises initially delivering liquid slip into such moldcavity at a relatively slow` rate in an amountl in'suilicient to lillsuch cavity but suiiicient to provide a liquid seal at the point ofintroduction, thereafter lling the mold cavity at a faster rate andunder such conditions that the slip supplied at the faster rateis'delivered out of contactwith the outside atmosphere and beneath thesurface of the liquid seal formed .by the slip fed at the slower rate,the Y slipv which is supplied at the faster ratebeing introduced intothe' mold cavity under superatmospheric pressure conditions.

8. A method of slip-casting a relatively flat and thin ceramic article,such as aplate or saucer which has a central disc-,like portion, asurrounding foot and an outwardly tapering rim portion and in which saidfoot constitutes the thickest portion of such article, which comprisesintroducing liquid slip into a closed mold cavity which, with dueallowance for shrinkage, has the size and shape of such article andcontrolling the introduction. of such slip into said mold cavity in suchmanner that the slip is fed into that portion of the mold cavity whichcorresponds to an eccentric point in said central portion but/adjacentsaid foot initially at a relatively slow rate for a portion of suchfilling operation and thereafter completing the filling of the moldcavity at a faster rate and nally supplying additional slip to said moldcavity to compensate for the absorption of water by said porous mold atthe rate at which said porous mold absorbs the water from said slip tocomplete the article.

9. A method of .slip-casting a relatively iiat and thin ceramic article,such as a plate or the thickest portion of such article, which comprisesintroducing liquid slip into a closed mold cavity which, with dueallowance for shrinkage, has the. size and shape of such article andcontrolling the introduction of such slip into said mold cavity in suchmanner that the slip is fed into that portion of the mold cavity whichcorresponds to an eccentric -point in said central portion but adjacentsaid foot initially at a relatively slow rate for a portion of suchfilling operation and thereafter completing the lling ci the mold cavityat a faster rate and finally supplying additional slip to said moldcavity to supply of additional slip occurs at substantially l0 normalatmospheric pressure.

JAMES A. BOWER.

